Unsaturated lower acids, including acrylic acids and methacrylic acids, are important organic chemical products. They are generally manufactured by a two-step oxidation of olefins, that is, partial oxidizing the olefins into aldehydes on an oxide catalyst containing molybdenum and bismuth, followed by further oxidizing the aldehyde products into corresponding acids on an oxide catalyst containing molybdenum and vanadium. Options such as increasing volume of the reactor or raising space velocity are applicable for enhancing the productivity of a manufacturing unit. Raising space velocity is certainly the most economic and convenient option.
There are a number of patents disclosing results on this field by various researchers.
JP-A-5-293389 discloses a catalyst represented by a formula of MoaBibFecAdXeYfZgSihOi, wherein Mo, Bi, Fe, Si, and O represent molybdenum, bismuth, iron, silicon and oxygen, respectively; A is at least one element selected from the group consisting of cobalt and nickel; X is at least one element selected from the group consisting of magnesium, zinc, manganese, calcium, chrome, niobium, silver, barium, tin, tantalum and lead; Y is at least one element selected from the group consisting of phosphorus, boron, sulfur, selenium, cerium, tungsten and titanium; Z is at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, cesium and thallium; and each of a, b, c, d, e, f, g, h and i represents the atomic ratio of each element, with the proviso that when a=12, b=0.01 to 3, c=0.01 to 5, d=1 to 12, e=0 to 6, f=0 to 5, g=0.001 to 1, and h=0 to 20, and i is the oxygen atom number needed to satisfy the atomic valence of each element. When gas-phase catalytic oxidation of propylene is performed by using the above catalyst to produce acrolein and acrylic acid, the yield of acrylic acid is 6.2 mole % under a propylene conversion ratio of 99.1 mole % and an acrolein selectivity of 89.6 mole %, the space velocity of propylene against the catalyst is 60˜90 hr−1(STP) during the process.
In Chinese Patent application CN93103817.1, Lanzhou Petrochemical Research Institute discloses a catalyst represented by a formula of MoBiFeWX1X2X3X4, wherein X1 is Co or Ni, X2 is at least one element selected from alkali metal or alkaline earth metal, X3 is at least one element selected from zinc, phosphorus, arsenic and boron, X4 is at least one element selected from silicon, aluminum, and titanium, based on the numbers of Mo atom being 12, the amount of Bi is 0.5˜4, Fe is 0˜8, W is 0˜4, X1 is 1˜8, X2 is 0.05˜3, X3 is 0˜4, and X4 is 0˜16. During the preparation of the catalyst, molybdenum oxide is used as a raw material to replace part of the ammonium molybdate raw material, and basic bismuth carbonate is used as a raw material to replace part of the bismuth nitrate raw material, and no pore-forming agent is necessary. The active ingredients are homogenously mixed with a silica micro-powder at a predetermined ratio, then silica gel is added thereinto and the mixture is band extruded, the extruded product is fired at 460° C. for 6 hours to produce the finished catalyst. Assessment on the catalyst is performed in a stainless steel pipe (Φ25.4 mm) packed with 1.0 L of the catalyst, a gas mixture with 10 wt % of propylene, 73 wt % of air and 17 wt % of steam is passed therethrough at a space velocity of 60 h−1(STP), acrylic acid and acrolein are produced with a yield of 93.2% under a propylene conversion ratio of 98.5% at a reaction temperature of 315° C., while the yield of COx is 4.2%.
In Chinese Patent application CN 00804787.1, BASF AG discloses a sphere-shaped or hollow-cylinder-shaped catalyst represented by a formula of Mo12BiaFebX1cX2dX3eX4fOx, wherein X1 is nickel and/or cobalt, X2 is thallium, an alkali metal and/or an alkaline earth metal, X3 is zinc, phosphorus, arsenic, boron, antimony, tin, cerium, lead and/or tungsten, X4 is silicon, aluminum, titanium and/or zirconium. Based on the number of molybdenum atoms being 12, a is from 0.5 to 4, b is from 0.01 to 5, c is from 0 to 10, d is from 0 to 2, e is from 0 to 8, and f is from 0 to 10. Assessment on the catalyst is performed in a stainless steel pipe (Φ26 mm) adopting an off-gas recirculating process at a space velocity of propylene being 120 h−1(STP), composition of the gaseous reactant comprises 6˜6.5 wt % propylene, 10.4˜10.7 wt % O2, 0.3˜0.5 wt % CO, 0.8˜1.2 wt % CO2, 0.025˜0.04 wt % acrolein and 3˜3.5 wt % steam, and balance of N2. The reactor applies an innovative method for two-stage temperature control, acrylic acid and acrolein are produced with a yield of 92.7% under a propylene conversion ratio of 94.5% when the temperature for the first reaction stage is 325° C. and the temperature for the second reaction stage is 347° C.
In Chinese Patent application CN 01116867, Nippon Shokubai Co., Ltd. discloses a hollow-cylinder-shaped catalyst represented by a formula of MoBiFeWX1X2X3X4X5, wherein X1 is cobalt and/or nickel, X2 is at least one element selected from alkali metal and thallium, X3 is an alkaline earth metal element, X4 is at least one element selected from zinc, phosphorus, arsenic, boron, thallium, antimony, tin, cerium, niobium, and manganese, X5 is at least one element selected from silicon, aluminum, titanium, and zirconium, based on the numbers of Mo atom being 12, the number of Bi atom is 0.1˜10, Fe is 0.1˜20, W is 0˜10, X1 is 2˜20, X2 is 0.001˜10, X3 is 0˜10, X4 is 0˜4, and X5 is 0˜30. Assessment on the catalyst is performed in a stainless steel pipe (Φ25 mm) at a space velocity of propylene being 115 h−1(STP), composition of the gaseous reactant comprises 7 wt % propylene, 14 wt % O2, 25 wt % steam, and balance amount of N2. Acrylic acid and acrolein are produced with a yield of 94.2% under a propylene conversion ratio of 98.5% at a reaction temperature of 310° C.
In Chinese Patent application CN 95115847, Mitsubishi Chemical Corp. discloses a hollow-cylinder-shaped catalyst represented by a formula of MoBiFeCoNiX1X2X3, wherein X1 is an alkali metal and/or thallium atom, X2 is at least one element selected from magnesium, calcium, zinc, cerium, samarium and halogen, X3 is at least one element selected from tungsten, phosphorus, arsenic, and boron. Based on the numbers of Mo atom being 12, the numbers of Bi atom is 0.5˜7, Fe is 0.05˜3, Co+Ni is 1˜10, X1 is 0.04˜2, X2 is 0˜2, X3 is 0˜3. Assessment on the catalyst is performed in a stainless steel pipe (Φ25 mm) at a space velocity of propylene of 90 h−1(STP), composition of the gaseous reactant comprises 10 wt % propylene, 73 wt % air, and 17 wt % steam. Acrylic acid and acrolein are produced with a yield of 95.1% under a propylene conversion ratio of 98.5% at a reaction temperature of 315° C.
In Chinese patent application CN 200480004485, Nippon Kayaku Co., Ltd. discloses a coated spherical catalyst represented by a formula of MoBiFeCoNiX1X2, wherein X1 is an alkali metal and/or thallium element, X2 is at least one element selected from tin, zinc, tungsten, chromium, manganese, magnesium, antimony and titanium. Based on the numbers of Mo atom being 12, the numbers of Bi atom is 0.1˜7, Fe is 0.5˜8, Co+Ni is 0.5˜20, X1 is 0˜1, X2 is 0˜2. Assessment on the catalyst is performed in a stainless steel pipe (Φ25 mm) at a space velocity of propylene being 90 h−1(STP), composition of the gaseous reactant comprises 8.3 wt % propylene, 14 wt % O2, 24.8 wt % steam, and balance of N2. Acrylic acid and acrolein are produced with a yield of 90.9% under a propylene conversion ratio of 98.1% at a reaction temperature of 330° C., while the yield of COx is 4.2%.
In most of aforementioned patents concerning catalysts for making aldehyde from unsaturated lower olefin, inventors adopt a process without off-gas recirculating with the highest space velocity of about 90 h−1(STP) except the 115 h−1(STP) in the patent of Nippon Shokubai, meanwhile, BASF AG utilizes a process with off-gas recirculating during propylene oxidation, wherein the volume space velocity of propylene relative to the catalyst can reach 120 h−1(STP). Raising the space velocity of olefin will cause various problems, which is particularly notable in non-off-gas-recycling processes, the most obvious problems are diminished yield and lower activity of the catalyst, in addition, overhigh temperature of the hotspot due to heat accumulation induced by increased heat generation, higher yield of COx and lower selectivity are apparent as well.